If you are looking for an IM post mortem PROCESS ( are you sure it's the process), then you can use your IM process template and just change information pertaining to roles, responsibilities, procedures, etc.

If not, you might want to google for any PIR template on the net and just make modifications relevenant to your environment.

You are correct. ITIL does not have an IM post mortem process...I am trying to create process and procedure documentation for handling a post mortem review of major incidents. I need to be more careful on how I use terms!

While I don't have a template, I would recommend ensuring that you capture Major Incident chronology and understand steps that were taken pre, during and post incident. In order to take any sort of action you will have to undertand very well what happened. Make sure all relevant parties are present.

Based on the findings you will have to build some sort of action plan to address the findings.

But whatever you do, ensure there is no fingure pointing, otherwise all people will be doing is laying blame on somebody else and covering their tracks.

We were discussing the same (Incidents-Post Mortem) last week as one of our client followed Major incident post mortem process.

ITIL doesn't speaks about this and also if its a major incident we can create a problem record (Problem management process) to identify the underlying root cause and have a permanent fix for the issue.